Generally, the industry of semiconductor manufacturing involves highly complex techniques for fabricating integrating circuits using semiconductor materials which are layered and patterned onto a substrate, such as silicon. An integrated circuit is typically fabricated from a plurality of reticles. Generation of reticles and subsequent optical inspection of such reticles have become standard steps in the production of semiconductors. Initially, circuit designers provide circuit pattern data, which describes a particular integrated circuit (IC) design, to a reticle production system, or reticle writer.
Due to the large scale of circuit integration and the decreasing size of semiconductor devices, the reticles and fabricated devices have become increasingly sensitive to defects. That is, defects which cause faults in the device are becoming increasingly smaller. The device can generally be required to be fault free prior to shipment to the end users or customers.
Various inspection systems are used within the semiconductor industry to detect defects on a semiconductor reticle or wafer. One type of inspection tool is an optical inspection system. In optical inspection systems, one or more radiation beams are directed towards the semiconductor wafer or reticle and a reflected and/or scattered beam is then detected. The detected beam is used to then generate a detected electrical signal or an image, and such signal or image is then analyzed to determine whether defects are present on the wafer.
Lasers are also used as light sources in many inspection systems to measure defects on reticles or wafers. Lasers provide light with high brightness and can provide a collimated beam of light that can be directed easily through lenses and toward the sample. Additionally, laser sources with a short wavelength, e.g., below 200 nm, may be advantageously used for examining relatively small feature sizes.
There is a continuing need for improved inspection techniques and apparatus having sub-200 nm light sources.